1. Field of the Invention
The invention relates to the field of monopole or dipole type broadband antennas (antennas with passive tuners).
It is applied, for example, to wire antennas in the context of telecommunications or jamming systems.
2. Description of the Prior Art
In broadband monopole (FIG. 1) or dipole type (FIG. 2) broadband antennas, the classic technique most commonly used to obtain satisfactory properties in a broadband consists in widening the poles by means of metal wires or strands, one for the upper pole and three for the lower pole.
A passive antenna tuner 2 makes it possible to refine the matching of the antenna with very wide frequency bands.
In this way, tactical, transportable (mountable and dismountable) antennas with a reduced wind-load area are obtained. A large number of strands ensures satisfactory omnidirectional properties in azimuth but entails penalties in terms of assembly time and wind-load constraints.
The matching is especially easy as the angle xcex1 (the angle between a radiating strand 1 and the vertical) is relatively great, generally ranging from 10xc2x0 to 45xc2x0. It is important to be able to match the antenna naturally with a given VSWR (voltage standing wave ratio) or SWR (standing wave ratio) typically ranging from 2 to 3, because this gives the antenna high efficiency while preventing high buffer (attenuator) values.
However, a big angle value, for example xcex1 greater than 15xc2x0, is often incompatible with the usual mechanical and operational constraints, such as wind behavior, weight, implementation time etc, especially at the relatively low frequencies (2-30 MHz high frequency band) or at the bottom of the VHF band (several tens of MHz) where the length of the radiating strands commonly ranges from a few meters to more than about 10 meters.
One solution used to compensate for these mechanical constraints lies in substantially strengthening the seatings of the radiating strands, especially for the radiating strands of the upper pole. This strengthening is accompanied however by major additional constraints of cost, transportation and tactical qualities of the antenna (namely, greater weight, increased mounting and dismantling time, the need for greater numbers of operators, bulkier infrastructures to take greater weight, greater wind-load area, etc.)
In the wire antennas of the prior art, therefore, the angles of inclination of the strands rarely exceed 15xc2x0 (the angle is taken with reference to the vertical axis of the figure). The matching is then adjusted with inductance-capacitance cells and by means of buffers or attenuators.
The object of the present invention relates to an antenna in which the extremities of the radiating strands are connected, for example, to their base or to the seating by means of a conductive wire capable of bearing the transmission power of the antenna. For example, the radiating strands of the upper pole are connected to the seating of the upper pole.
The invention relates to a wire antenna comprising one or more radiating strands, said strands being connected to a seating, wherein at least one of said strands has a first end connected by means of a conductive wire to said seating or connected to its second end.
The radiating wire forms part, for example, of the upper pole of the antenna and the connecting wire is a metal wire or a Teflon(copyright)-coated metal wire.
The invention relates for example to the monopole or dipole type antennas used for example in the HF, VHF or UHF bands ranging from some MHz to some hundreds of MHz.
The antenna according to the invention has the following advantages in particular:
improved efficiency as compared with the usual wire antennas,
preservation of its tactical qualities and ease of use,
the additional cost of the metal wires connecting the upper strands to the seating of the pole is negligible as compared with the total cost,
a novel architecture that entails no penalties for the implementation of the system or for the antenna mounting and dismantling time,
negligible extra weight and space requirement for the metal wires,
improved stability of the strands when they are relatively long (several meters) and flexible under wind stresses, and consequently a stabilizing of the radiation at the top of the band where there are risks of flattening of the antenna patterns through the variable incurvation of the upper strands,
the addition of metal wires optimizes the matching of the antenna through the forming of thick strands, thus bring about a substantial improvement in the efficiency of the antenna (the buffers/attenuators needed have lower values).